Aromatic polycarbonate resins are well known and have long been used in molding compositions for the preparation of tough, dimensionally stable articles. The chemistry, synthesis, properties and applications of polycarbonates are extensively discussed in the manuscript Chemistry and Physics of Polycarbonates, by Schnell, Interscience, 1964 and Polycarbonates by Christopher and Fox, Reinhold, 1962.
Although polycarbonates have some inherent flame resistance, increasingly more stringent requirements for improved flame resistance are reflected in issuance of the large number of patents relating to this technology. Among the methods to improve flame retardance mention may be made of the addition or incorporation of large amounts of halogen (U.S. Pat. Nos. 3,751,400; 3,382,207 and 3,334,154). In U.S. Pat. No. 3,775,367 there is taught adding of an organic and/or an inorganic metal salt to the polycarbonate resin.
Additions of perfluoroalkane sulfonic acid salts of alkali metals and organic alkali salts of carboxylic acids have been disclosed in U.S. Pat. No. 3,836,490 and in U.S. Pat. No. 3,775,367. Also noted is German Published Patent No. 2,149,311 which discloses the use of insoluble alkali metal salts, particularly salts in inorganic acids phosphonic acids and sulphonic acids. Flame retardant polycarbonate compositions containing alkali metal salts or an inorganic acid are disclosed in U.S. Pat. No. 4,223,100. U.S. Pat. No. 3,535,300 discloses the use of small amounts of specified metal salts (which do not include alkali metal salts) in combination with halogen carried on the polymeric backbone or on an additive. U.S. Pat. No. 4,110,299 teaches adding of alkali or alkaline earth metal salts of organic acids in combination with additives such as inorganic halide and an organic monomeric or polyemic aromatic or heterocyclic halide improve the flame retardancy of an aromatic polycarbonate.
Also noted are the teaching in regard to the drip suppression of the compositions when they are exposed to a flame. In German Patent No. 2,535,262 there is a teaching to add fluorinated polyolefins such as polytetrafluroroethylene (PTFE) to a polycarbonate containing organic alkal metal salt to retard dripping. U.S. Pat. No. 4,110,299 discloses adding to a polycarbonate resin fluorinated polyolefin, fibrous glass or a siloxane, in combination with certain salts and an inorganic halide to diminish tendency to drip. In PCT application WO 80/00084 there is disclosed-in Example 13-a blend of aromatic polycarbonate and a block copolymer of polycarbonate and polydimethylsiloxane (57%/43%) and including sodium salt of trichloro benzene sulfonic acid. The blend was noted to have improved resistance to stress crazing. The document generally discloses improved ductility, solvent resistance and flame retardance characteristic of blends of polycarbonates and a block copolymer of polycarbonate and polydiorganosiloxane.
Also relevant in this context is U.S. Pat. No. 4,880,864 which disclosed adding a metal salt of an inorganic acid to a polydiorganosiloxane copolycarbonate for improving the flame retardance of the resin. A flame resistant, impact modified polycarbonate resin was disclosed in U.S. Pat. No. 4,786,686. The improved composition is said to include a rubbery polymer containing residual ethylenic unsaturation and a fluorine containing polymer of the fibril forming type as additions to the polycarbonate resin.